The present invention refers to an improved apparatus and a related process for blow molding preforms of thermoplastic material, in particular such an apparatus as generally described in the Italian patent application no. PN98A000042 filed by this same Applicant.
The peculiarities of the apparatus described in the above-cited patent application lie in the fact that it is provided with:
a plurality of pairs of mutually joinable half-moulds, which are associated to an appropriate, preferably revolving structure for handling said half-moulds, and preform support devices corresponding to said half-moulds,
a preform feeding mechanism to deliver an orderly sequence of preforms held at an appropriate blow-moulding temperature into the respective pairs of half-moulds kept in their opened position and associated to said rotary member.
a pick-up device adapted to recover the finished container from the respective pair of half-moulds upon the opening thereof.
an opening and clamping mechanism adapted to clamp the half-moulds together after they have moved through the position of the preform feeding mechanism, and to open them before they move through the position of the pick-up mechanism for removing the finished container, in which said pairs of half-moulds are constituted by a stationary half-mould and a moving half-mould capable of being opened from and clamped against said stationary half-mould.
In particular, said stationary half-moulds are substantially joined to said structure, which is preferably rotating about a vertical axis, and are arranged in a substantially vertical position, with the moving half-moulds adapted to be clamped against the respective stationary half-moulds with a substantially rotary movement having a horizontal axis of rotation.
The other general construction and use characteristics of the apparatus according to the present invention are thoroughly described in the afore cited Italian patent application no. PN98A000042, to which reference should therefore be made.
Anyway, to the purpose of favouring a better and readier understanding by a reader, the origin of and the technical-industrial ground on which said patent is based are briefly recalled here. In practice, it has been originated by the fact that, according to prior-art techniques, the blowing moulds in an in-line arrangement turn out to be particularly critical, since with increasing blow-moulding pressures, as well as with increasing numbers of cavities contained in each single pair of blow-moulding plates, increasingly rapid and powerful pumping stations are required. Furthermore, the increased overall pressure generated by the bottles during blow moulding must be contrasted by a correspondingly greater mould clamping pressure.
However, such a pressure, which is not only considerably higher, but also pulsating, has a negative effect also on the actual resistance of the same moulds, which are not only caused to undergo a greater pressure, but are at the same time required to withstand such a greater pressure on a longer arm, considering the greater number of blowing gates, and this of course makes their rigidity more critical and their tendency to deform outwardly much more likely, with easily imaginable effects on the quality of the blow-moulding process and the blow-moulded bottles themselves.
Furthermore, when blowing moulds provided with a great number of cavities are used, the time required to transfer all preforms into the respective cavities increases proportionally, and his of course causes the whole cycle time to INCREASE under a clear reduction in the productivity of the moulding apparatus.
Just in view of doing away with these drawbacks, the practice is known from the disclosures in the publications U.S. Pat. No. 3,596,315-U.S. Pat. No. 4,233,022-EP 0 596 487- U.S. Pat. No. 4,850,850 and U.S. Pat. No. 4,313,720 of using to preform blow moulding purposes apparatuses that are adapted to rotate about a vertical axis in a carousel-like manner, in which the outer sides are occupied by a plurality of blowing half-moulds capable of opening from and camping against each other in an orderly and sequential manner. However, in these apparatuses it is actually both half-moulds that are driven to move. They furthermore move in a so-called xe2x80x9cbook-likexe2x80x9d manner, in that each one of them moves about a respective vertical axis.
Apparatuses of this kind are connected with generally known drawbacks and construction complications, since both half-moulds must be handled to move synchronically. Furthermore, the fact that they open in a horizontal direction, and therefore by widening apart, makes it necessary for the entire carousel-like arrangement to be sized correspondingly; it in particular requires apparatuses to be used which are significantly larger and, therefore, more awkward to be handled and installed.
In view of doing away with the problems connected with the use of moving half-moulds rotating about respective vertical axes, an apparatus of the kind described in the afore mentioned Italian patent application has been disclosed.
Nevertheless, even this kind of apparatus has still some problem left with it and offers margins for further improvement, which may be summarized as follows:
the need for the neck of the preform to be locked in place, ie. clamped with a mould (the half-moulds) makes it necessary for the same preform to be released from its transferring means only upon the half-moulds being completely clamped together, this of course requires that the related operations be carried out in series, ie. in a sequence, under resulting greater usage of time, which of course contributes to an increased overall cycle time and, therefore, a marked reduction in the performance capabilities and the general productivity of the entire apparatus;
furthermore, upon the final container having been blow-moulded, the opening of the mould quite frequently gives rise to a slight displacement of the respective container and this makes much more difficult for an appropriately provided pick-up and unloading member to engage the neck portion of the container and then transfer the same container into the next station.
From U.S. Pat. No. 4,035,463 it is known a method and an apparatus for blowing preforms in a rotary table (EIII) with blow molds. Each of said blow molds consists of two symmetrical halves (62), supported by a commmon vertical spindle, so that said halves are misplaced in the horizontal plane. Furthermore, the preforms are previously heated and positioned in a concurring rotary table (EII) and the transfer from said heating table (EII) and the blowing rotary table (EIII) is carried out by a rotary station (D) where rotation axis is vertical, as the vertical spindle (55). However, if a blowing machine is used, having blowing halves, one of which is fixed and oriented outwards, the other being rotatable on an horizontal spindle (instead of a vertical spindle), the technical arrangement and solution described in the cited U.S. patent can not be used due to the interference between said station (D) rotating horizontally and the halves blow mold rotating vertically.
Based on the above considerations, it is therefore a main purpose of the present invention to provide the blow moulding apparatus for the production of hollow bodies, as well as the operating mode thereof, in such a manner as to enable its productivity to be increased by the effect of an accelerated movement of the blowing half-moulds.
A further purpose of the present invention is to make it possible for the blow-moulded container to be firmly and reliably held in position when the respective half-moulds are opened.
The apparatus and the method according to the present invention shall furthermore be capable of being implemented with the use of currently available techniques and, therefore, shall be reasonably low-cost, reliable and preferably capable of being integrated with a preform production stage situated upstream.